With the acceleration of urbanization, large-scale construction and renewal projects inevitably generate massive amounts of urban waste soil. This waste soil is typically categorized into two types based on its usability: High-quality waste soil, characterized by excellent compaction performance, can be directly reused in scenarios like road subgrade filling or site backfilling—common examples include gravel soil and silty sand. In contrast, low-quality waste soil, such as soft clay and organic soil, has high water content and poor mechanical properties, making direct utilization extremely challenging.

Regrettably, approximately 80% of urban waste soil is currently disposed of through unscientific methods: simple open-air stacking occupies valuable land resources, enclosure-based sea reclamation disrupts coastal ecosystems, and illegal dumping poses severe environmental pollution and geological safety risks. The Central Ecological and Environmental Protection Inspectorate has repeatedly highlighted that the illegal disposal of construction muck and slurry—key components of low-quality waste soil—remains a prominent issue hindering urban ecological protection.

Traditional approaches to urban waste soil recycling suffer from obvious inefficiencies and environmental drawbacks. For high-quality waste soil, the reuse is often limited to low-value applications like landfilling or rough site leveling, failing to tap into its potential for high-grade construction scenarios. For low-quality waste soil, pre-treatment via solidification or sintering is required before reuse; however, these technologies are plagued by high energy consumption, excessive carbon emissions, and sensitivity to raw material variability—all of which prevent large-scale industrial application.

This disconnect between waste soil generation and scientific recycling not only wastes a valuable secondary resource but also exacerbates the contradiction between urban development and environmental protection.

To tackle these challenges, co-processing technology has emerged as a holistic solution, seamlessly integrating waste soil characteristic analysis, technical standardization, and equipment optimization—with the twin shaft mixer and rotary screen serving as the core pillars of this efficient workflow.

1. Precision Analysis of Waste Soil Core Traits

The first step in co-processing is conducting a rigorous evaluation of waste soil properties. For high-humidity, high-viscosity waste soil (a typical low-grade variant), laboratory tests and on-site sampling confirm that muck with a moisture content of 30%-60% and a plasticity index ≥25 poses the greatest treatment hurdles. During crushing, this muck tends to clump and generate excessive dust, requiring equipment R&D to prioritize airtight designs—such as fully enclosed casings—to curb emissions without compromising efficiency. A key post-crushing requirement is that particle size must be below 20mm to ensure compatibility with subsequent mixing and screening processes, a goal that depends on tight coordination between crushing equipment and the rotary screen. This synergy ensures that only properly sized material enters the next stage, laying the groundwork for the twin shaft mixer to operate at peak performance.

2. Defining Core Technical Indicators for Co-Processing

Clear technical standards are essential for effective co-processing, and three key metrics stand out—all directly linked to the performance of the twin shaft mixer and rotary screen:

Mixing Uniformity: The blending of waste soil and curing agent must reach over 95% (minimum 90%), a benchmark achievable exclusively through the high-efficiency stirring of a twin shaft mixer. Unlike single-shaft alternatives, the twin shaft mixer's counter-rotating shafts generate intense shearing and tumbling forces, ensuring even dispersion of curing agent particles even in highly viscous waste soil.

Curing Agent Ratio: Dosage must be precisely controlled at 5% ± 0.5% of the waste soil’s weight, using high-precision electronic scales and flow meters integrated into the feeding system—critical for optimizing the twin shaft mixer's reaction efficiency.

Post-Processing Screening: After mixing, the treated material must pass through a rotary screen to remove uncrushed clumps or impurities. The rotary screen's adjustable mesh size and continuous rotation guarantee that only qualified 20mm-sized material proceeds to reuse applications like brick-making or road construction, preventing quality flaws that would otherwise arise from subpar screening.

3. Specialized Equipment for High-Humidity, High-Viscosity Waste Soil

Efficient treatment of this challenging waste soil type relies on a purpose-built equipment lineup, with the twin shaft mixer and rotary screen at its center:

Crushing Stage: A crusher with staggered shear blades breaks down large lumps, effectively cutting through sticky agglomerates to avoid clogging—ensuring a steady feed for the subsequent twin shaft mixer.

Mixing Stage: Crushed material is immediately conveyed to the twin shaft mixer, where pre-metered curing agent (delivered by the automatic feeding system) is added. The twin shaft mixer’s dual shafts enable rapid, uniform blending, reducing mixing time by 30% compared to single-shaft models and minimizing curing agent waste through full reaction with the waste soil. This step is pivotal, as the twin shaft mixer's performance directly dictates the quality of the final product.

Screening Stage: The mixed material is fed into a rotary screen, whose inclined design and variable speed control enable efficient separation of qualified fines from uncrushed residues. The residues are redirected back to the crusher for reprocessing, maximizing resource utilization—all made possible by the rotary screen's reliable classification capabilities.

Dust Control and Intelligent Monitoring: A negative-pressure ventilation system above the crusher and rotary screen collects dust to meet environmental standards. Meanwhile, sensors on the twin shaft mixer and rotary screen monitor real-time data, including mixing uniformity, curing agent dosage, and rotary screen mesh throughput. If deviations occur (e.g., uneven mixing or excessive residue), the automatic control system adjusts the twin shaft mixer's rotation speed or the rotary screen's mesh size instantaneously, ensuring consistent processing quality. The twin shaft mixer and rotary screen thus not only drive operational efficiency but also enable the intelligent oversight that is critical for modern, eco-friendly waste soil treatment.

Urban waste soil, once viewed as a burden, can be transformed into a valuable resource through co-processing technology. The twin shaft mixer and rotary screen, as core equipment in this workflow, address the key pain points of low-quality waste soil treatment: the twin shaft mixer ensures efficient, uniform mixing, while the rotary screen guarantees post-processing quality. By integrating these devices with intelligent control systems, urban waste soil recycling can achieve both environmental benefits (reduced pollution and land occupation) and economic value (cost savings in raw material procurement), paving the way for sustainable urban development.